Rutin was isolated from dried leaves and flowers of buckwheat (Fagopyrum esculentum Moench.). The effects of rutin on angiotensin II-induced hypertrophy of cultured cardiac myocytes and proliferation of cardiac fibroblasts of neonatal rats were evaluated by analyzing the cell surface area, measuring the protein synthesis rate through 3H-leucine incorporation, and the MTT method. Rutin (0.8 to 8.0 mg/l) exhibited a strong inhibition on the hypertrophy and proliferation. The results suggested that rutin from buckwheat flowers and leaves might have protective effects on cardiac hypertrophy.Colegio de Farmacéuticos de la Provincia de Buenos Aires